One of the core principles of homeopathy is let like cure like. In practical terms that means we use remedies made from substances, which in larger amounts, would cause similar symptoms. Just think what happens to you when you chop up a strong onion and you can see why a homeopathic remedy made from onion might be useful for hayfever. Another example is that a remedy made from coffee might be appropriate for helping someone with insomnia.
This principal of like cures like is also used in conventional medicine but not as frequently as in homeopathy. In patients who are in a persistent vegetative state there have been some successes when they have been given sleeping pills.
A very recent example is of children in the USA with extreme peanut allergies who have been given small amounts of peanut protein in liquid or powder form. Initially they are given the equivalent of one thousandth of a peanut and this amount is slowly increased over time. Four children who have completed years of the treatment are now able to tolerate 13 to 15 peanuts without showing even mild symptoms.
DO NOT TRY THIS AT HOME IF YOU HAVE A CHILD WITH A NUT ALLERGY
Another case of like cures like, and one with a strong homeopathic connection, is the use of radiation to treat tumours. Dr Emil Grubbe developed blistering and tumours on his hands and neck while he was experimenting with X Rays as a student at the Hahnemann Homeopathic Hospital in Chicago in the 1895. As the radiation was very clearly the cause of the tumours one of the professors suggested it might be a useful therapeutic tool in treating cancers. Dr Grubbe was the first person to use radiation therapy on Mrs Rose Lee for breast cancer in 1896 and she benefited from this treatment. For reasons which remain unclear, he is often referred to as a radiologist, physicist or doctor but his homeopathic connections and credentials rarely get a mention!